1. Field of the Invention
The present invention is related to digital wireless telecommunications and, in particular, to a method and apparatus for processing the handover of voice and data calls between networks configured to different telecommunications standards.
2. Description of the Related Art
One of the most widely-used digital wireless telecommunications standard is the Global System for Mobile communications (GSM) standard, developed by the European Telecommunications Standards Institute, which utilizes time division multiple access (TDMA) techniques. The GSM standard is incorporated herein by reference. A GSM-compliant wireless communication system includes a radio access network, known as a base station subsystem (BSS), comprising a plurality of base transceiver stations (BTSs) for transmitting and receiving radio frequency (RF) signals from a subscriber""s mobile station (MS) (e.g., a cellular phone, a pager, a portable computer, etc.), and at least one base station controller (BSC) for managing radio resource and routing signals to and from the BTSs. Each BTS is constructed to transmit and receive signals from within a predetermined geographic region called a cell. In accordance with the GSM standard, the system further includes a fixed or core network having a circuit switched (or voice switching) portion for processing voice calls and a packet switched (or data switching) portion for supporting bursty, high speed data transfers such as, for example, e-mail messages and web browsing. The circuit switched portion includes a mobile-services switching center (MSC) that switches or connects telephone calls between the radio-access network (i.e., the BSS) through a BSC, and a subscriber""s public switched telephone network (PSTN) or a public land mobile network (PLMN). The MSC is connected to a BSC through a standard interface known as the A-interface that requires signaling messages between the BSC and the MSC to be arranged in a particular order and format. The packet-switched portion, also known as General Packet Radio Service (GPRS), includes a Serving GPRS Support Node (SGSN), similar to the MSC of the voice-portion of the system, for serving and tracking the MS, and a Gateway GPRS Support Node (GGSN) for establishing connections between packet-switched networks and a mobile station. The SGSN may also contain subscriber data useful for establishing and handing over call connections. The core network also includes a home location register (HLR) for maintaining xe2x80x9cpermanentxe2x80x9d subscriber data and a visitor location register (VLR) (and/or a SGSN) for xe2x80x9ctemporarilyxe2x80x9d maintaining subscriber data retrieved from the HLR and up-to-date information on the location of the mobile station.
A handover, as defined herein, is the process of automatically transferring a communication transaction (e.g., a call) in progress from one cell to another cell to avoid adverse effects of movements of a mobile station. A detailed description of the handover procedure(s) can be found in xe2x80x9cThe GSM System for Mobile Communicationsxe2x80x9d by Michel Mouly and Marie-Bernadette Pautet, 1992 (ISBN: 2-9507190-0-7). The entire disclosure of this publication is incorporated herein by reference.
Thus, as an MS travels from cell to cell while conducting a telephone call, the BSC switches the MS from one BTS to another, based on signal measurement reports from the MS, by executing a handover procedure consistent with the GSM standard. As the MS travels further and further away from the original BTS, handover would occur between adjacent BSCs, and even between neighboring MSCs. In a similar fashion, as an MS maintains a packet-switched portion while traveling from one cell to another, the handover would occur between adjacent SGSNs. Thus, voice and data calls can be established and maintained, so long as the MS travels within an area serviced by the GSM network.
Problems occur, however, when a subscriber desires to switch between a GSM network and another wireless network such as, for example, a network configured to the Universal Mobile Telephone Service (UMTS) standard, which employs recently developed wide-band code division multiple access (W-CDMA) techniques for paired spectrum bands and TD-CDMA for unpaired bands. The UMTS standard is incorporated herein by reference. A UMTS compliant system typically comprises a core network (CN) and a UMTS Radio Access Network (URAN) that includes a ground-based portion. The ground-based portion of the radio access network (RAN) is often referred to as the UMTS Terrestrial Radio Access Network (UTRAN) and comprises a radio network controller (RNC) and a base station (BS), having similar functionality as the BSC and the BTS of a GSM network respectively. New radio interfaces have been specified for communication between different UMTS subsystems such as, for example, the Iu interface between UTRAN and CN, which are different from those interfaces used by GSM devices.
Heretofore, handover of a call has been based only on uplink and downlink radio transmission quality (e.g., data bit error rate) between the mobile station and neighboring cells of the serving network or a neighboring network to avoid dropping the call. However, current systems do not provide efficient support for initiating a handover in a situation where a subscriber desires to use another network based not only on radio transmission quality but also on performance parameters such as, for example, data transmission rate, and/or subscription services available to the user.
Accordingly, there is a need for handling the handover of calls between different communication networks based on, for example, subscriber preferences when the MS is capable of and permitted to utilize the different networks.
An object of the present invention is to initiate handover of a communication transaction between different mobile telecommunication networks based on user and/or network specified parameters.
An advantage of the invention is that the radio access network (e.g. BSS or UTRAN) is provided with additional guidance or requirements from a user and/or the user""s service provider of a handover of a communication transaction from a serving wireless network to a neighboring wireless network, when the mobile station is in a region covered by the different networks. As defined herein, the neighboring wireless network may cover a region adjacent to, overlapping with, or within that covered by the serving network.
According to one aspect of the invention, the core network such as, for example, the MSC, the SGSN, and/or an integrated MSC/SGSN having functions of both the MSC and SGSN is provided with information relating to the capabilities of an MS to operate within a multitude of networks, the connection properties required or desired by the MS, and subscription services available to the user of the MS. This information is transmitted to a controller of the radio access network such as, for example, a base station controller of a GSM network or a radio network controller of a UMTS network so as to further assist the controller in determining whether a call (voice or data) may be handed over to another network. The controller may also utilize the information to determine whether the MS may initiate a call within a particular network.
According to another aspect of the invention, a multi-mode mobile station capable of communicating with different wireless networks sends a signaling message to a core network node (e.g. an MSC, SGSN or MSC/SGSN) indicating its capability to operate in various network environments. The signaling message is preferably a binary number having at least two logical values for indicating whether the mobile station can support radio access to another network such as, for example, a UMTS network. The binary number may be incorporated in an information element compliant with the GSM standard such as the GSM Mobile Station CLASSMARK 3 information element. The core network node also retrieves and/or analyzes information relating to, for example: (a) quality of service (xe2x80x9cQoSxe2x80x9d) (e.g. voice quality) requested by the mobile station during setup, (b) network congestion, (c) location of the mobile station, etc. MSC (or SGSN) then sends to the controller of the radio access network a signaling message (e.g. a recommendation or command) incorporating the above information so as to assist the controller of the radio access network portion in determining whether to initiate a handover to another network. The controller of the radio access network may also utilize information relating to network congestion and location of the mobile station to determine whether a handover is to be executed.
In one embodiment, a message is sent from a mobile station to the serving wireless network, which includes an indication that the mobile station is capable of communicating with the neighboring wireless network. The message may also include the requisite connection properties, and/or parameters indicating the permission or preference of the user to utilize various networks. Information relating to the communication characteristics of the neighboring wireless network is sent from the serving wireless network to the mobile station. Using the information relating to the communication characteristics of the neighboring wireless network, the mobile station receives radio signals from the neighboring wireless network. The quality of the radio signals between the mobile station and the neighboring wireless network is measured. The serving wireless network sends a message to the neighboring wireless network to request a handover of the communication transaction, provided the quality of the radio signals between the neighboring wireless network and the mobile station meets one or more predetermined handover criteria or a predetermined minimum threshold. The predetermined handover criteria or threshold may be defined such that the to-be-established connection will be of a service quality specified by the user. A handover of the communication transaction from the serving wireless network to the neighboring wireless network is executed after the neighboring wireless network has established a communication channel for the mobile station pursuant to the handover request.
In another embodiment, execution of the handover is also based on previously stored subscription data relating to the preference or permission of the user to utilize the neighboring wireless network.